1. Field of the Invention
The present invention relates to a content data storage device which uses a nonvolatile memory, like a NAND flash memory, to erase data in block units and stores content data, such as video and audio, and relates to a control method of the storage device.
2. Description of the Related Art
A NAND flash memory that is a nonvolatile memory is characterized by large capacity and low price. Therefore, the NAND flash memory is widely used for a digital camera, a digital audio player, etc. NAND flash memory has characteristics such as its writing rate is slow and the size of a block that is the erasing unit of stored content data is large. For using the NAND flash memory as a consumer electronic device, the characteristics do not make matter. However, for using the NAND flash memory to a content data storage device for broadcasting, the characteristics should be considered to be improved.
Generally, the content data storage device needs to erase the data stored therein for each content item. Therefore, the content data storage device stores one item of content data in a storage space in the NAND flash memory, of which a capacity is integral multiple of its one block size. If the content data is one with a wide band like a moving image, the capacity of the content data is larger than the block size of the NAND flash memory. Thus, the waste of the capacity of the NAND flash memory is low through a method of storing the content data in the storage space in the NAND flash memory having the capacity of integral multiple of the block size. On the other hand, if the content data is one with a narrow band, like a still image and audio, etc., the capacity of the content data is smaller than the block size. Thereby, the waste of the capacity of the NAND flash memory is large through the aforementioned method when the narrow-band content item is written in the storage space.
If the content data is audio, because the capacity thereof is small, the content data storage device cannot write any data in the NAND flash memory until an audio data of one page that is a writing unit is supplied. Since the writing rate of the NAND flash memory is slow, even when inputting audio data has been terminated, the content data storage device does not terminate the writing immediately. That is, in the case of use of the content data storage device in a situation in which the content data includes a moving image of a wide band-content items, audio and a still image of a narrow-band content items, if there are many narrow-band content items, it turns into an issue that the use efficiency of the NAND flash memory is extremely deteriorated and the writing speed of the content date becomes slow.
Meanwhile, as for a method of compensating the low speed of the writing in the NAND flash memory in the conventional content data storage device, connecting a plurality of NAND flash memories in parallel is proposed. However, since the connecting the plurality of NAND flash memories in parallel enlarges the block size that is the erasing unit of the content data storage device in comparison with the case of a single memory IC, the size of the block that is a matter in writing data in the NAND flash memory becomes serious.
An example, which effectively utilizes a memory area of a storage medium by recording moving images in clusters of large sizes and still images in clusters of small sizes in recording the moving images and the still images in the storage medium, has been disclosed (e.g., refer to Jpn. Pat. Appln. KOKAI Publication No. 2005-352899).
An example, which effectively utilizes a partially unoccupied memory by setting identification codes corresponding to writing and reading units for audio data and video data to manage each data, has been disclosed (e.g., refer to Jpn. Pat. Appln. KOKAI Publication No. 10-13777).